In conventional lighting systems, individual light sources are typically hung from trusses or fixed structural members mounted in front of the stage, at the sides of the stage or over the stage. The light sources are adjusted to direct the light beam to a desired location on the stage and are then secured in that position by tightening bolts or other fasteners. A large sealed beam lamp of 1,000 to 1,500 watts run from a 110 volt AC line is typically employed to create the light. In addition to generating visible light, such lamps, generally noted as par lamps, generate a significant amount of infrared heat.
In a typical stage lighting plan, the light sources are employed in either of two fashions. Certain light sources may be used as a wash or general stage illumination. The remainder of the light sources are used as spots for highlighting specific positions on the stage, such as an actor's face.
The light beams emanating from each light source may be colored by the use of a colored celluloid gel. The gel is positioned within a frame which is slid into a receiver positioned at the end of the light source so that the beam passes through the colored gel. The gel functions to absorb the incident light other than the color desired. The absorbed light is transformed into heat which warps and discolors the gel, requiring frequent replacement as often as once every show.
Shutters are typically pivoted at the end of the light source to block out selected portions of the light beam to shape the incidence of the beam on the stage. In many cases, a mechanical iris may be provided in the light source to control the beam divergence. When a light source is used as a wash, a wide beam divergence is desired. However, when used as a spot, the light beam preferably is narrowed to a very small divergence.
The intensity of the light beam emanating from each light source is individually controlled by a large power dimmer. The power dimmers, in turn, are controlled by the main lighting control panel. The typical lighting system therefore requires a massive array of electrical cables, including cables connecting the control console with a power dimmer and cables interconnecting the power dimmer with the associated light source. It has also been found that the use of power dimmers to control the intensity of light has induced chop in the AC power line supplying the entire theater. This has been found to induce undesirable noise, such as distortion, hum etc. particularly during the performance of rock groups employing instruments relying on electrical input.
A typical performance, such as a rock concert or theatrical performance, may require a hundred or more individual lighting cues or lighting formats during the performance. Up to 500 separate lights may be necessary to light the entire performance. Usually 25% of these lights are used as wash and the remainder are used as specials. The large number of lights are necessitated as the light position, color, intensity and divergence must be preset prior to the performance.
Attempts have been made to automatically control a stage lighting system during a performance. U.S. Pat. No. 3,898,643 to Ettlinger, issued Aug. 5, 1975, discloses a system including a memory for storing the intensity level of the lights for each cue during a performance. The system may then set the intensity of the light through conventional power dimmers in an automatic sequence. However, this device merely transfers the manual operation of power dimmers to an automatic system which, while relieving an operator of substantial work during the performance, necessitates still more complex and costly equipment in the system.